The present invention relates to an image display device which utilizes emission of electrons into a vacuum produced between a front substrate and a rear substrate, and in particular to a configuration of a support member which seals and supports the front and rear substrates with a desired spacing therebetween.
Conventionally, color cathode ray tubes have been widely used as display devices excellent in producing high-brightness high-definition display devices. However, as the video quality in information processing equipment and TV broadcasts has been improved in recent years, the demand has been becoming stronger for flat panel display devices capable of realizing lighter weight and thinner profile in addition to the performance of high brightness and high definition. As their typical examples, liquid crystal display devices and plasma display devices have been put to practical use.
Further, various types of flat panel type display devices are under development for practical use. Especially as display devices capable of realizing higher brightness, image display devices are being developed which utilize emission of electrons into a vacuum from an electron source (for example, they are ones called electron-emission type display devices, field emission type display devices or FEDs). Organic electroluminescent (EL) display devices are also being developed which feature low power consumption.
Among the display devices utilizing the emission of electrons, of such flat panel type display devices, known are one employing an electron-emitting structure invented by C. A. Spindt et al.; one employing an electron-emitting structure of the metal-insulator-metal (MIM) type; one employing an electron-emitting structure utilizing an electron emission phenomenon due to the tunnel effect in the quantum theory (this electron-emitting structure is sometimes called the surface conduction type electron source); and one employing an electron-emitting structure utilizing an electron emission phenomenon exhibited by a diamond film, a graphite film or carbon nanotubes.
Among these flat panel type display devices, an electron-emission type image display device has a rear substrate having, on an inner surface thereof, cathode wirings or lines provided with electron-emission type electron sources and control electrodes, and a front substrate having anodes and phosphors on an inner surface thereof opposing the rear substrate. The front and rear substrates are attached together with a support member sandwiched between their peripheries, and are hermetically sealed to form a panel. The airtight space within the panel is exhausted to a pressure lower than the atmospheric pressure or to a vacuum. The control electrodes are disposed such that the direction of extension of the control electrodes is intersect the direction of extension of the cathode wirings with an insulating layer or an insulating spacing interposed between the control electrodes and the cathode wirings. Further, to maintain the spacing between the rear and front substrates at a desired value, spacing-maintaining members are interposed between the rear and front substrates. The spacing-maintaining members are formed of thin plates of glass or ceramics, for example, and are stood upright and clear of pixels.
FIG. 8 is a cross-sectional view of a major portion of an image display device serving as an example of conventional flat panel type display devices of this kind. This image display device comprises: a rear plate (a rear substrate) 2 having a plurality of electron-emissive elements 5 thereon; a front plate (a front substrate) 1 disposed to oppose the rear plate 2 and having thereon image-forming members 6 which form images by radiation of electron rays emitted from electron-emissive elements 5; a support frame 3 which is sandwiched between the front plate 1 and the rear plate 2, and supports peripheral portions of the front plate 1 and the rear plate 2; and spacers (spacing-maintaining members) 4 disposed between the front plate 1 and the rear plate 2 so as to serve as props. The front plate 1 and the support frame 3, the front plate 1 and top ends of the spacers 4, the rear plate 2 and the support frame 3, the rear plate 2 and bottom ends of the spacers 4 are fixed together by using glass frit 7, respectively.
In a case where the width of peripheral portions of the support frame 3 is reduced as a means for reducing the weight of an image forming device having a large-sized screen, known is a method which makes outer sides of peripheral portions of a support frame 3 convex toward the outside of a display area of the image forming device without making the width of the peripheral portions of the support frame 3 uniform, but with the corner portions being formed to have the minimum width, as shown in a perspective view of its major portion illustrated in FIG. 9. The image-forming device of this kind is disclosed in Japanese Patent Application Laid-Open Publication No. Hei 7-302558.